Boiler water treatment



Patented Feb. 3, 1953 STATES RATENT OFFICE 2,627,502 Beltran wa raa TauA' -M NT laul G gBj ird, Western Springs, I ll assignor to National Aluminate Corporation, Chicago, 111., a curpor'ation of Delaware Ho Drawing. Appiioation May 7, 1949, S eria-l No. 92,999

l I "5 2- 1ilp'e tiearsl ie a m 0f Pre n ing or minimizingcorrosi'on"clue to ext ema steam generatoraand stea'rfn'liries.

Dissolved gases, larlyoxygen, are receeie d w J cejrresi on in steam generating equipment. Corrosion dueto oxygenkan be eee'cuvei controlled by carefuily reducing the" oxygen coritent of the fedwa'ter supplied to the steam. generator. 'Ifhis'is' commonly done by 'one or a combination ofthe following processes: deaeration, deaetivation, and chemicalabsorption.

In the latter process, 'a material such as sodie uni sulfite or a tannin is introduced mm the feedwater'and reacts chemically with the dis solvedoxygenI Sodium sulfite removes the oxyen by combining with it to form sodium'sulfate.

There are two principal disadvantagesjhowever, in the use'of sodium sulf te. in" the first place, its use" increases the dissolved solids in the boiler water, and it may sufierundesirabl e decompositions at high pressures and teniperae tur'es, resulting either in the appearance of; sule fur dioxide, in the steam ei ie'prouuced; or in reduction to the sulfide. Secondly, if it is added tofthe feedwater before the" feedvvater passes through the deaeratoig'a substantial excess must be employed because thesodium sulf te reacts with some of the oxygen before the water'reaches the deaerator.

It is an object of this invention to provide an improved process for the chemical absorption of dissolved oxygen from boiler ieedwater wherein no undesirable dissolved solids are added to the water.

It is a further object to provide a chemical treatment for boiler feedwater which may be ad ed to the sedwa e ahe d e t eat atv nd wh s wi pass the d ae ter i substee: i v unreaq ed s a e tenab e o a bin a the temperatures subsequently encountered, the oxygen not removed by the" deaerator.

Still a further object is to provide a material to be added to boiler feedwater for the chemical absorption of oxygen which will be converted, by oxidation, to a material which is of value in the boiler from the standpoint of scale prevention. Other objects will appear hereinafter.

I have now found that phosphites are valuable oxygen absorbents for use in. boiler feedwater, and possess several important advantages over hitherto used materials. Phosphites are par ticularly effective in steam generators operating at pressures of 300' pounds per square inch (p. s. i.) and over, and the corresponding temmost G mmon causes 6r (Cl. FEES-23.)

iii

sulfite, with which the art is already'f 2v 'ese are e ati ly iner in he all): sense of a catalyst, temp ture's gem employed n feedwa s Q ecause of. this iiert ess phqsehites y be d ed to th eed a er be or it s B tt the deaerator and after. the tee h h dee r r it W l b ow is 191 .1 ntia l t 11119 1 3 q eieellr The phosphi s h n ava able is a s scav n d n th 1 99??? am. in 1 he remaining oxy n Whit? Wa 0 maven y he dea rat ra d a mieqrtaet dvant e. in the ar of rhe s. a ti a y in g per t n a PYESSWBS; of 309 1 1?. f i'a l 3 10 0 3 0 9- sn is th t th plates a qnvst t9 R Q P rth ha e re ult n rv l t able m the s andpq nt Q? 5 manly due t it bil ty t We. orthophosphate in the boiler. mm nl used i gh 19 p r y of the o di a 21 a kal m ta-. rich?- phosphites, hypophosphite and m hosp are u a le M t cqmm e 9t dium a as sii n PDQ ydrate, Na2HPQ35H2O s u n orthq hqs sodium aci rthqnhesr tiaiizlOaHzQ an ium emi osphite N HBQ'Q see v e id i t h b l d e 2 m ca le U The m n 9i an of the e h sphite re quired for oxygen absorption;calculated'iriter s of Nazi-IP05, is the same'astheamount ofs'o i tin S 1 1iii' l t an 2 9 n i i t ad ieu' h he is)? We at a point after the daerator'so'that ar amtumtrebout 10" to 510 parts p (n. pl' m) by weight, will be in "tai boiler waterIL' Similar ex ses of hosp te been'found to represent good operating practice. In general, the addition of 1 to 10' p. p. m. of anhydrous sodium phosphite to the ieedwater, on a weight basis, or the chemically equivalent amount of one or more of the phosphite compounds previously mentioned, will provide the oxygen absorption desired and give the desired excess. Larger amounts are not, however, detrimental except that it is often undesirable to increase the dissolved solids in the boiler water more than necessary.

In the addition of phosphates to high pressure boilers, it is common practice to add them to the boiler drum as contrasted to addition to the feed lines. Thismode of addition of the phosphites may also be used, and oxygen absorption in the boiler thereby obtained.

The preferred method of introducing the phosphites into the boiler water is to feed them along with other treating chemicals, such as carbonates, phosphates and organic substances, such as tannin, starch, lignins, lignin derivatives and the like.

The phosphites are preferably used in boiler waters where some degree of alkalinity is desired, that is to say, boiler waters operated at a pH over 7.0. In case high alkalinity is desired in the boiler water, the disodium phosphite salt is preferably used, while if lower alkalinities are desired the primary phosphite or phosphorous acid are preferably employed.

While the hereinabove described practices relate principally to steam generation at pressures of about 300 p. s. i. and above, and the corresponding temperatures, it should be pointed out that the phosphites can be used as oxygen absorbents at lower pressures and temperatures if a small amount of cobalt is used therewith as a catalyst. Quantities of cobalt (calculated as metal) of the order of 0.05 to 0.1 p. p. m. by weight of the feedwater are generally adequate.

Instead of cobalt catalysts other catalysts which increase the rate of reaction of phosphites with oxygen can be employed. In general, the

Where a catalyst is used to catalyze the reac- 5-:

tion of oxygen with an alkali metal phosphite to form an alkali metal phosphate the quantity required is, extremely small and will usually be a fraction of one part per million by weight calculated'on the basis of the metallic component of the catalyst added to the feed water. In general, the quantity used is preferably within the range of 0.05 to 0.50 p. p. m. by weight of the feed water.

The" invention is hereby claimed as follows:

1. A method of generating steam in steam boilers operating below about 300 pounds per square inch but above the boiling point of water,

which comprises incorporating with the feedwater to the boiler where the steam is generated or;

1 to 10 parts per million by weight of an alkali 4 metal phosphite and 0.05 to 0.5 part per million by weight, calculated as the metal, of a cobalt salt dissolved in said water.

2. An alkaline water for steam generation containing 10 to 50 parts per million by weight of an alkali metal phosphite, calculated as NazHPOs, said Water also containing a fraction of one part per million by weight of a dissolved cobalt salt, said quantity of cobalt salt being at least 0.05 part per million parts of said water and being suificient to accelerate the reaction of oxygen with said phosphite to form phosphates when steam is generated by boiling said water at steam pressures below about 300 pounds per square inch.

3. A method of generating steam in steam boilers operating below about 300 pounds per square inch but above the boiling point of Water which comprises adding to the feed water to the boiler where the steam is generated 1 to 10 parts per million parts of water by weight of an alkali metal phosphite and a quantity of a catalyst from the group consisting of manganese salts, copper salts, nickel salts and cobalt salts, said salts being soluble in said Water and being effective to catalyze the reaction of oxygen with phosphites to form phosphates, and boiling said water under said steam generating conditions, the quantity of said salts being sufficient substantially to reduce said oxygen corrosion.

i. A method of generating steam in steam boilers operating under steam generating conditions where oxygen corrosion normally occurs which comprises incorporating with the feed water to the boiler where the steam is generated 1 to 10 parts per million by weight of an alkali metal phosphite and at least 0.05 part of cobalt sulfate, calculated as cobalt, per million parts of said water, and boiling said water, the quantity of said cobalt sulfate being suflicient substantially to reduce said oxygen corrosion.

5. An alkaline boiler water containing. 10 to 50 parts per million by weight of an alkali metal phosphite, calculated as Nazi-IP03, said water also containing a quantity of dissolved cobalt sulfate, said quantity being at least 0.05 part of cobalt sulfate, calculated as cobalt, per million parts of said water and not substantially more than about 0.5 part of cobalt sulfate per million parts by Weight of said water.

PAUL G. BIRD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,345,323 Frazer et a1 June 29, 1920 1,841,825 Kriegsheim Jan. 19, 1932 2,046,303 Rice June 30, 1936 OTHER REFERENCES Chemical Abstracts, vol. 22, page 4321, 1928; vol. 28, page 3678, 1934.

Inorganic and Theoretical Chemistry, by Mellon-vol. 8, 1928, page 905. 

3. A METHOD OF GENERATING STREAM IN STEAM BOILERS OPERATING BELOW ABOUT 300 POUNDS PER SQUARE INCH BUT ABOVE THE BOILING POINT OF WATER WHICH COMPRISES ADDING TO THE FEED WATER TO THE BOILER WHERE THE STEAM IS GENERATED 1 TO 10 PARTS PER MILLION PARTS OF WATER BY WEIGHT OF AN ALKALI METAL PHOSPHITE AND A QUANTITY OF A CATALYST FROM THE GROUP CONSISTING OF MANGANESE SALTS, COPPER SALTS, NICKEL SALTS AND COBALT SALTS, SAID SALTS BEING SOLUBLE IN SAID WATER AND BEING EFFECTIVE TO CATALYZE THE REACTION OF OXYGEN WITH PHOSPHITES TO FORM PHOSPHATES, AND BOILING SAID WATER UNDER SAID STEAM GENERATING CONDITIONS, THE QUANTITY OF SAID SALTS BEING SUFFICIENT SUBSTANTIALLY TO REDUCE SAID OXYGEN CORROSION. 